Conventionally, a high-tension bolt or a high-tension strength bolt is used for tightening structural members with each other while constructing a bridge, an iron frame construction, or the like. The high-tension bolt is tightened by a bolt tightening tool (shear wrench) disclosed in, for example, laid-open Japanese Patent Application Publication No. 2004-001233.
The shear wrench includes a housing, a circuit board, a commutator motor accommodated in the housing, a drive transmission mechanism, an inner socket, an outer socket, and a trigger. When an operator pulls the trigger, the commutator motor is driven, and the inner socket fitted to a tip of the high-tension bolt is rotated by way of the transmission mechanism, and the outer socket fitted to a nut is rotated in a direction opposite to the rotational direction of the inner socket. As a result, the high-tension bolt is tightened.